Conventionally, a display device is known including a plurality of pixels formed above a substrate. A LCD (Liquid Crystal Display) and OLED (Organic Light Emitting Diode) display are typical examples of such a display device. In particular, in recent years, the development of OLED displays having excellent response characteristics and viewing angle characteristics is progressing rapidly.
An OLED display is a display device with a light emitting element using an electroluminescence phenomenon arranged in each pixel. A display device using an organic light emitting layer as a light emitting element is called an organic EL (Electro Luminescence) display device. This type of display device can emit light in at colors of various wavelengths by selecting the light emitting material which forms the light emitting layer.
Generally, each pixel formed above a substrate includes a light emitting element and a drive transistor which supplies a current for driving the light emitting element. After a drive transistor is formed above the substrate, the drive transistor is covered by an insulation layer formed from an organic resin material and a light emitting element is formed above the insulation layer. The insulation layer is used as a planarized film for relieving undulations caused by the transistor. For example, a display device having the structure described in Japanese Laid Open Patent No. 2014-142641 is typically known.